Interobserver variability of CT angiography for evaluation of aortic annulus dimensions prior to transcatheter aortic valve implantation (TAVI).

OBJECTIVE: Assessment of aortic annulus dimensions prior to transcatheter aortic valve implantation (TAVI) is crucial for accurate prosthesis sizing in order to avoid prosthesis-annulus-mismatch possibly resulting in complications like valve dislodgement, paravalvular regurgitation or annulus rupture. Contrast-enhanced multidetector computed tomography allows 3-dimensional assessment of aortic annulus dimensions. Only limited data exist about its interobserver variability. METHODS: In 100 consecutive patients with symptomatic severe aortic stenosis (51 male, BMI 27±5kg/m(2), age 81±7 years, heart rate 72±15bpm, Logistic Euroscore 31±14%, STS-Score 7±4%), pre-interventional aortic annulus assessment was performed by dual source computed tomography (collimation 2×128×0.6mm, high pitch spiral data acquisition mode, 40-60ml contrast agents, radiation dose 3.5±0.9mSv). The following aortic annulus characteristics were determined by three independent observers: aortic annulus maximum, minimum and mean diameters (Dmax, Dmin, Dmean), eccentricity index (EI), effective aortic annulus diameter according to its circumference (Dcirc), effective aortic annulus diameter according to its area (Darea), distance from the aortic annulus plane to the left (LCA) and right coronary artery (RCA) ostia, maximum (DmaxAR) and minimum aortic root diameter (DminAR), maximum (DmaxSTJ) and minimum diameter of the sinotubular junction (DminSTJ). Subsequently, interobserver variabilities were assessed. RESULTS: Correlation between the three observers showed moderate to close agreement (between r=0.67 and r=0.97, all p<0.001). Mean differences (SE) between the three observers ranged from 0.07 (0.06)mm to 0.24 (0.07)mm for assessing the mean AA diameter (Dmean), from 0.28 (0.04)mm to 0.60 (0.06)mm for determining the effective AA diameter derived from the annulus area (Darea) and from 0.03 (0.07)mm to 0.07 (0.11)mm derived from the AA perimeter (Dcirc). For measurements of LCA and RCA distances to the AA level, mean interobserver differences (SE) ranged from 0.36 (0.07)mm to 0.76 (0.09)mm and from 0.15 (0.06)mm to 0.45 (0.11)mm. CONCLUSION: Computed tomography provides reproducible measurements of the aortic annulus and root geometry in patients scheduled for TAVI. The perimeter-derived aortic annulus diameter shows the lowest interobserver differences. Interobserver variabilities in prosthesis size recommendation were further reduced, if all three sizing methods were considered and stated as a "consensus result".

Cone-beam CT using a mobile C-arm: a registration solution for IGRT with an optical tracking system.

A method for registering images acquired from a prototype flat panel mobile C-arm, capable of kilovoltage (kV) cone-beam computed tomography (CT), to a linear accelerator (LINAC) isocenter is presented. A calibration procedure is performed which involves locating reflective markers placed on the C-arm and a phantom in two coordinate systems. A commercial optical tracking system locates the markers relative to the LINAC isocenter (room coordinates). The cone-beam imaging capabilities of the C-arm provide the location of the markers on the calibration phantom in image coordinates. A singular value decomposition (SVD) algorithm is used to determine the relationship between the C-arm, image coordinates and room coordinates. Once the calibration is completed, the position of the C-arm at any arbitrary location is accurately determined from the tracking system. A final transformation is calculated capable of mapping voxels in the reconstructed image set to their corresponding position in room coordinates. An evaluation to determine the accuracy of this method was performed by locating markers on a phantom. The position of the phantom markers in room coordinates was obtained directly using the optical tracking system and compared with that using the described method above. A mean absolute distance of 1.4+/-0.5 was observed for a completely transformed image set. This is comparable to that of systems routinely used for image-guided radiation therapy (IGRT).

Recovering the X-ray projection geometry for three-dimensional tomographic reconstruction with additional sensors: attached camera versus external navigation system.

Three-dimensional tomographic reconstruction using intra-operative mobile C-arms could provide physicians with new and exciting tools for image-guided surgery. Recovery of the projection geometry of mobile X-ray systems is a crucial step for such reconstruction procedures. Recent work on medical imaging describes the use of optical or electro-magnetic sensor systems in order to navigate surgical instruments. These systems can also be used for the estimation of C-arm motion, and therefore for the recovery of the projection geometry of the X-ray C-arm. In this case, the mathematical problem that needs to be solved is equivalent to the hand-eye calibration well studied by both the computer vision and robotics community. We first study the recovery of the motion and projection geometry using five different hand-eye calibration methods proposed in the literature. The optical navigation system POLARIS from Northern Digital Inc. was used in our experiments. The results of the estimated motion and projection geometry using the five hand-eye calibration methods are compared with the same results obtained using an off-the-shelf CCD camera attached to the mobile C-arm. The experimental results include three-dimensional tomographic reconstruction results using our mobile C-arm. We show that even though the motion of the C-arm is more precisely recovered using the navigation system, the projection geometry is better estimated using the attached CCD camera.

Urinary mutagenicity in vegetarians and people on a mixed-western diet.

This investigation was undertaken to determine whether the consumption of an ovolacto-vegetarian diet and a mixed-western diet by a group of 31 and 32 persons respectively resulted in the excretion of different levels of mutagens in the urine of these two dietary groups. All subjects were male participants of the "Deutschlandlauf 1987" and consumed strictly controlled diets with limited energy supply and a defined protein/fat/carbohydrates relation. 24-h Urines were collected before the start of the race, mutagens were extracted by a combination of the XAD-2 method of Yamasaki and Ames (53) and the blue-cotton method of Hayatsu et al. (20), and aliquots were assayed for mutagenicity with Salmonella typhimurium strains TA 98 and TA 1538 in the presence of an activating system (S 9-mix). Urinary mutagenicity was significant but at considerable variance in 26 (13) vegetarians and non-vegetarians as estimated with strain TA 1538 (TA98). No statistically significant difference could be detected between the vegetarian and the mixed-western dietary groups in any urinary mutagenicity parameter given below. In detail the following mean values were obtained: 2.46 +/- 1.87 his+ revertants/ml urine, 3,333 +/- 1,835 revertants in 24-h urines, and 5.01 +/- 3.1 revertants/mg creatinine for vegetarians and 3.13 +/- 2.18 his+ revertants/ml urine, 4,611 +/- 5,913 revertants in 24-h urine, and 8.98 +/- 20.17 revertants/ml creatinine for non-vegetarians with S. typhimurium TA 98 and 3.75 +/- 2.88 his+ revertants/ml urine, 6,094 +/- 7,885 revertants in 24-h urine, and 10.88 +/- 21.14 revertants/mg creatinine for vegetarians and 4.17 +/- 2.71 his+ revertants/ml urine, 5,705 +/- 4,421 revertants in 24-h urines, and 6.97 +/- 9.29 revertants/mg creatinine for non-vegetarians with strain 1538. Considerable individual variation in levels of urinary mutagenicity in spite of consumption of identical, controlled diets may at least in part depend on inherent differences of absorption, metabolism, and excretion patterns of mutagens by individuals, preventing collective comparisons of the extent of exposure to dietary mutagens.